The general rule of thumb is no more than she can cover at one time. My bantam Silkies can do maybe 6 LF eggs up to 11 Bantam eggs. It just depends on the size of the hen so there isn't a solid and hard rule here. My LF hens do 11 LF eggs easy.
You should still candle by week 2(10 or so days) and pull the dud eggs to make life easier on her as well. I can usually spot live ones by then and I am inexperienced.